1. Field of the Invention
This invention generally relates to the fabrication of integrated circuit (IC) devices, and more particularly, to a hydrogenated oxide interface on silicon and a method for forming the same using high-density hydrogen plasma.
2. Description of the Related Art
The quality of polysilicon thin films and the interface between silicon and silicon dioxide (Si/SiO2) layers are critical to the performance of thin film transistor, MOS capacitors, and various ICs. A hydrogenation process is generally carried out to passivate the dangling bonds in polysilicon layers, and in the interface between the polysilicon and gate insulator (silicon oxide) films. Conventional hydrogenation approaches introduce hydrogen at the grain boundaries and Si/SiO2 interfaces using either a forming gas anneal (FGA), or a plasma hydrogen treatment. The diffusion of hydrogen through a device is dependent upon the device structure, physical and chemical characteristics of the constituent layers, and the thermal state. The forming gas anneal process typically involves heating the device in an atmosphere of molecular hydrogen (4-10%) and nitrogen gas. The FGA process is highly inefficient for the low temperature devices due to very low rate diffusion kinetics. As a result, the FGA is typically carried out at temperatures exceeding 300° C. The FGA thermal budget strongly depends on the temperature, and is significantly higher than a plasma-based process. The forming gas anneal process typically requires a high thermal budget to properly enhance polysilicon and Si/SiO2 interface characteristics. Due to the high thermal budget, the forming gas annealing process is not efficient for high throughput commercial applications.
The plasma hydrogen processes are much more efficient than FGA for the introduction of hydrogen at the polysilicon grain boundaries and Si/SiO2 interface. A stable and reliable Si/SiO2 interface is critical for the fabrication of advanced display devices and other integrated circuits. The quality of the SiO2/Si interface is dictated by the quality of the SiOx transition layer at the interface and the defects in the poly-Si layer. The general approach is to improve the quality of the SiOx transition layer at the Si/SiO2 interface. Defects in the poly-Si can also be passivated and the stoichiometry improved by oxidation and hydrogenation processes. A hydrogen plasma is generated between coupled electrodes. However, the limitations associated with coupled electrodes prevent the generation of an especially reactive hydrogen species. A high throughput commercial plasma hydrogenation fabrication requires further decreases in the temperature and thermal budgets to process low temperature, large area, integrated circuits and liquid crystal displays (LCDs).
Although lower temperatures are generally desirable for any device fabrication process, they are especially critical in LCD manufacture, where large-scale devices are formed on a transparent glass, quartz, or plastic substrate. These transparent substrates can be damaged when exposed to temperatures exceeding 650 degrees C. To address this temperature issue, low-temperature Si oxidation processes have been developed. These processes use a high-density plasma source such as an inductively coupled plasma (ICP) source, and are able to form Si oxide with a quality comparable to 1200 degree C. thermal oxidation methods.
It would be advantageous if a process could be developed to enhance the hydrogenation of polysilicon film and Si/SiO2 interfaces at a significantly lower thermal budget and temperature, as compared to the above-mentioned conventional hydrogenation processes.
It would be advantageous if low-temperature plasma processes could be developed for hydrogenation, comparable to the high-density plasma oxidation processes.
It would be advantageous if the low-temperature plasma oxide and hydrogenation processes could be carrier out in-situ, as a continuous process.